When a conventional flow meter is removed from the pipe wherein the fluid to be measured flows, at the time of maintenance were an investigation when there is a problem, or the like, the flow of the fluid to be measured within the pipe is stopped and the pressure is released (see, for example, Japanese Unexamined Patent Application Publication 2002-310767 (“JP '767”).
Furthermore, the flow path structure used in a conventional flow meter, as illustrated in FIG. 8, comprises: a base 50 wherein a secondary flow path block 52 for forming a secondary flow path is formed integrally on the outer peripheral surface of a main flow tube 51; a seal plate 54 for sealing the opening portion of the secondary flow path block 52, having a measurement hole 53 in the center portion thereof: a circuit board 55, stacked on the seal plate 54, having, on the bottom surface thereof, a flow rate detecting element that is inserted into the measurement hole 53; and a cover 56 for covering the opening portion of the secondary flow path block 52. Note that the seal plate 54 and the circuit board 55 are secured by screws to the secondary flow path block 52.
Furthermore, as illustrated in FIG. 9 and FIG. 10, the base 50 of the flow path structure is structured from: a flat L-shaped introduction vertical channel 62 for elevating the fluid that flows in from the measurement hole 61; a first secondary flow path 63 and a third secondary flow path 65 that are formed parallel to the main flow tube 51: a second secondary flow path 64 and a fourth secondary flow path 66 that are formed in a direction that is perpendicular to the main flow tube 51; and an expulsion vertical channel 67 for expelling the fluid from an expelling opening 68 into the main flow tube 51. The introduction vertical channel 62 has a flat L shape, and thus a portion of the fluid that has been introduced flows in the direction that is opposite to the flow of the main flow tube 51, and because dust and the like has a greater mass than expected, the dust, and the like, has a difficult time flowing in the opposite direction, so that the dust, and the like, flows through the first secondary flow path 63 to the expulsion vertical channel 67. A portion of the fluid that is introduced flows through the 2 second secondary flow paths 64, and after confluence, connect to the third secondary flow path 65. A detection region with a narrow width is formed so as to correct nonuniformity of the flow of the fluid, through narrowing the flow path through having protruding portions 69a, which are provided on partitioning walls 69, which are provided on both sides of the third flow path 65, face each other. The fluid, after detection, branches into a fourth secondary flow paths 66, to connect with the expulsion vertical channel 67. Finally, the fluid connects to the main flow tube 51 through the expelling opening 68. (see, for example, Japanese Unexamined Patent Application Publication 2006-308518 (“JP '518”.)